SAO PAULO— President Dilma Rousseff's approval rating sank by 27 percentage points in the last three weeks, a poll showed on Saturday, the strongest evidence yet that the recent wave of street protests sweeping Brazil poses a serious threat to her likely re-election bid next year.

The share of people who consider Rousseff's administration "great" or "good" plummeted to 30 percent from 57 percent in early June, according to a Datafolha opinion poll published in local newspaper Folha de S.Paulo.

The drop was the sharpest for a Brazilian leader since 1990, when Fernando Collor outraged the population by freezing all savings accounts in a desperate attempt to stop hyperinflation. Two years later, Collor resigned the presidency as Congress moved to impeach him over corruption allegations.

Until recently, Rousseff had enjoyed some of the highest approval ratings of any leader in the Western world, largely thanks to record-low unemployment. But her popularity started to slip in early June as rising consumer prices began to eat away at Brazilians' purchasing power, a sure recipe for trouble in a country with a long history of runaway inflation.

Then came the nationwide street demonstrations of the past few weeks, which have sent shockwaves through Brazil's political establishment. While the protests have not been directed at a single leader or party, widespread discontent with a ruling class that is seen as self-serving and corrupt is eroding the popularity of politicians at all levels, including Rousseff.

The Datafolha poll was the first taken since more than a million Brazilians poured on to the streets in recent weeks to protest a litany of grievances, from corruption and poor public services to outrage at billions of dollars in taxpayer money being spent to host the 2014 soccer World Cup.

The president's approval rating fell sharply in all regions of the country, the poll showed. In the Northeast, birthplace of her popular predecessor Luiz Inacio Lula da Silva and a stronghold of the ruling Workers' Party (PT), the share of people who view the administration favorably sank to 40 percent from 64 percent in a poll on June 8.

The poll also asked Brazilians if they were in favor of the protests, the largest to hit Brazil in two decades. Eighty-one percent of respondents said they support the demonstrations. Asked if the protests had resulted in positive changes, 65 percent said yes.

The unrest has prompted a flurry of promises to improve public services and other measures aimed at quelling the protests. In the past week alone, Brazil's Congress voted on a battery of bills promoting issues popular with the protesters, and the Supreme Court ordered the arrest of a lower house representative convicted of corruption.

Rousseff shocked Brazil on Monday by proposing a constituent assembly to overhaul the country's political system, but withdrew the plan a day later after it ran up against widespread opposition, even from within her own party.

She is now seeking congressional support for a non-binding plebiscite to ask Brazilians how they would like to see the political system changed. In the Datafolha poll, 68 percent of respondents said they backed the idea of a plebiscite.

The drop in Rousseff's popularity comes at a delicate moment for Brazil's economy, which barely expanded last year and relies on an ambitious agenda of infrastructure projects to return to sustained growth in coming years.

The approval rating of Rousseff's economic team, led by Finance Minister Guido Mantega and central bank president Alexandre Tombini, dropped to 27 percent from 49 percent.

The Datafolha poll, which was conducted on June 27-28, surveyed 4,717 people and has a margin of error of plus or minus 2 percentage points.

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